North Korea dismissed the allegation Thursday that it attacked a South Korean Navy vessel in March as "sheer fabrication," warning that punitive measures over the incident would be met with "tough measures including an all-out war."

The statement issued by Pyongyang's National Defense Commission (NDC) came in response to the findings of a multinational investigation team that probed the March 26 sinking of the frigate Cheonan.

"They are pointing a dirty accusing finger at us like a thief," an unidentified spokesman for the NDC said. The commission is headed by North Korean leader Kim Jong-il.

Calling President Lee Myung-bak a "traitor," the statement also offered to dispatch a delegation of North Korean investigators to Seoul to check the veracity of the international findings.

"We remind the group of traitors in advance that there should be not a shred of doubt about the material evidence to be produced before the inspection group," the statement said.

It promised a "merciless strong physical blow," if South Korea responds with even a minor act of aggression on its territory.

The attack on the Cheonan is speculated to be retaliation for a naval skirmish that occurred last November, when a North Korean boat crossed the maritime border and exchanged fire with a South Korean vessel before retreating in flames.